EFFECT OF SWARD HEIGHT DURING LATE PREGNANCY ON INTAKE AND PERFORMANCE OF CONTINUOUSLY STOCKED JUNE-LAMBING AND AUGUST-LAMBING EWES

Herbage organic matter intake (OMI), grazing behaviour and ewe and lam b production were measured during the last 4 weeks of pregnancy in 2-y ear-old and mixed-age Border Leicester x Romney ewes due to lamb in Ju ne (winter) or August (spring). The intake of herbage (averaged across lambing date groups) was 1.4+/-0.1, 1.7+/-0.1, 1.7+/-0.1 and 1.9+/-0. 1 kg OM ewe-1 day-1 (mean +/-s.e.m., P < 0.01) for ewes continuously s tocked on 10-year-old ryegrass (L. perenne) and white clover (T. repen s) pastures maintained at sward surface heights (SSH) of 2.0, 4.0, 6.0 and 8.0 cm respectively. Ewes that were in a good body condition scor e achieved their required daily intake of energy at a SSH of 2.0 cm. R elative to ewes on the 8.0 cm SSH treatment, those on the 2.0, 4.0 and 6.0 cm SSH treatments attempted to increase intake by increasing graz ing duration rather than biting rate. Ewe liveweight, condition score, midside wool growth rate and mean fibre diameter were not affected by sward surface height in either lambing group. There was no within sea son effect of SSH on lamb birthweight, but lambs born in June were lig hter than lambs born in August (4.4+/-0.2 v. 5.3+/-0.2 kg, P < 0.001). This trial has shown that, at the same SSH, June-lambing pregnant ewe s achieve a similar daily herbage intake to that of August-lambing ewe s. A target SSH of 2.0 cm during the last month of pregnancy was shown to be appropriate for both August- and June-lambing ewes in good cond ition. However, for August-lambing ewes in poor condition, a SSH of 2. 0 cm at this stage of pregnancy would be detrimental to overall produc tion, particularly in terms of ewe liveweight loss.